In nearly all milled or fabricated refiner plates, and in many cast refiner plates, the working surface of the refiner plate consists of clusters of parallel bars and grooves. The refiner filling disc is normally depicted as a complete circle, but in fact the filling often consists of several more-or-less pie-shaped segments which are much easier to handle when replacing a filling.
U.S. Pat. No. 5,740,972 discloses improvements in replaceable refiner fillings and the manufacture of refiner fillings with working surfaces using relatively narrow, closely spaced bars on the working surface of the plate. The refiner fillings have relatively thin blades separated by shallower spacer bars having a thickness which determines the width of the grooves.
The refiner fillings use a metal or other hard and durable material for the blades and spacers, which blades and spacers are then metallurgically bonded to each other along their entire intercontacting surfaces. A suitable metallurgical bond is achieved through any of several known methods including welding, diffusion bonding, brazing, or any other method which results in a joint strength approaching that of the blade or spacer material. Materials used include stainless steel blades bonded to carbon steel spacers and ceramic and metal composite materials as blade or spacer components in refiner fillings. A metal composite material which exhibits suitable strength and toughness characteristics for a particular refiner application is used for the blades of the filling, while a much less costly material may be used for the spacers.
As disclosed in the '972 patent, segmental replacement disc refiner plates are produced with segments having both non-circular edges (i.e., side edges) which are not precisely radial. Instead, the side edges are oblique to the precisely radial line such that the refiner plate segmental dividing line is parallel to the adjacent refiner blade. Each segment may typically have a value of 30, 45, or 60 degrees of a circle so that 12, 8, or 6 segments, respectively comprise a refiner disc.
The blades of each cluster are positioned parallel to a side edge of the cluster and extend from the outer periphery toward the inner periphery of the segment. Blade obliqueness to the disc radius increases with distance normal to the side edge. It is desirable with refiner plates to avoid shallow crossing angles (i.e., high degree of obliquity to radial) of stator and rotor blades and therefore desirable to maintain blade obliqueness in a range of 3 to 20 degrees with respect to disc radial. Hence, the blade pattern is begun anew at that location in the refiner segment where increasing obliqueness approaches 20 degrees. So, the segment blade pattern is repeated at intervals to maintain blade obliqueness within a desired range over the entire working surface of a refiner filling. The repeated blade pattern is defined herein as a blade cluster characterized by a common cluster angle throughout the refiner filling.
An obvious method for producing the components of a blade cluster for this type of fabricated refiner plate would consist of cutting individual blades and spacers, such that for any specified set of inside diameter, outside diameter, and cluster angle, each blade and spacer would have a unique length. The uniqueness of each component, and the relative difficulty of fitting them precisely, results in a high cost to manufacture.
The present invention provides refiner fillings of the kind disclosed in the '972 patent and methods for manufacture of the fillings economically and efficiently with very significant reduction in the cost of tools and fixtures while greatly facilitating the assembly of refiner filling clusters. In particular, the invention facilitates the manufacture of refiner fillings in a preferred embodiment having a preferred range of working surface blade obliqueness to disc radial, working surface blades assembled in cluster units conforming to the range of blade obliqueness, a fixed pumping angle, and a fixed number of identical segments comprising a refiner filling.
The invention also provides a barset envelope or parallelogram as defining a basic unit of manufacture of a working surface of blades and spacers, with each barset divisible into two identical blade clusters.